On Performance of Cooperative OFDM System with Subcarrier Number Modulation

5G and beyond systems demand exceptional spectrum efficiency (SE) and rapid data transmission for long-haul communications. Originating from 4G, orthogonal frequency division multiplexing (OFDM) also carries forward to future technologies due to promising system performance. Conversely, SE can be further improved by effectively integrating index modulation (IM) variants. OFDM sub carrier number modulation (SNM) is one of the potential IM approaches and an appealing choice as it uses the adaptive number of active sub carriers to transmit more information compared to conventional IM techniques. Further, incorporating OFDM-SNM with cooperative relaying improves the system's reliability and SE for long-haul communications. This paper investigates the end-to-end pairwise error probability (PEP) for a dual-hop cooperative relay-assisted OFDM-SNM system. Further, the analytical PEP results for the decode-and-forward (DF) relaying system are validated using the Monte Carlo simulation. It is also shown that beyond 22 dB SNR, the considered approach outperforms the conventional OFDM while offering substantial SE gain.